Hydrazides of amino-polyacetic acids as chelants

ABSTRACT

Amino-polyacetic acids such as ethylenediaminetetraacetic acid, diethylene triaminepentaacetic acid and nitrilotriacetic acid are reacted with alkanols and then with hydrazine to form the hydrazides which may be converted to carboxyhydrazides, i.e. carbazic acids. The products perform well as chelants and sequestering agents.

This is a division, of application Ser. No. 522,068, filed Aug. 10, 1983now U.S. Pat. No. 4,609,757.

The present invention relates to the provision of a novel sequesteringagent which performs like, but superior to, ethylenediaminetetraaceticacid with regard to speed, cost, and operating pH.

Where hard water, sea water, corrosion product, or mill scales have beendeposited in pipes and on other equipment it is known to remove suchdeposits by contact with an aqueous solution of sequestering agents ofwhich aminopolyacetic acids have been widely used, e.g.ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, andnitrilotriacetic acid. Similarly, the presence of such sequesteringagents in water systems will help prevent the deposit of such scales.These agents perform satisfactorily but require reasonably long contacttimes and pH's (either acidic or alkaline, depending on the scale to bedissolved) that can be corrosive to the substrate from which the scaleis to be removed.

It is accordingly an object of the present invention to provide a novelsequestering agent which performs more quickly and at more acceptablepH's, rendering its use more economical overall.

In accordance with the present invention there is provided a novelsequesteringchelating agent comprising a hydrazide of anamino-polyacetic acid, e.g. nitrilotriacetic acid or an alkylenepolyamino-polyacetic acid such as ethylenediaminetetraacetic acid ordiethylenetriaminepentaacetic acid. The hydrazide can be a simplehydrazide of hydrazine per se or can be a carboxyhydrazide, i.e. acarbazic acid, produced by reacting the terminal --NH₂ groups withalkali metal carbonates.

The invention also extends to the manner of preparing such hydrazides,to compositions containing them and their use.

Hydrazides are advantageously prepared from the aminopolyacetic acids byesterification with a lower alkanol such as methanol or ethanol to formthe ester. Advantageously less than the stoichiometric amount isemployed, e.g. at most about 0.5 times the stoichiometric amount ofacetic acid groups and preferably about 0.3 to 0.45 times, the partialester thereby being formed. The reaction proceeds in water even atmoderate temperatures, e.g. about 100° F.

Substantially simultaneously therewith or subsequent thereto, hydrazineis added, advantageously in from 1.3 to 1.5 times the stoichiometricamount of the acetic acid groups, and the reaction mass is heated for along time, e.g. 195° F. for 24 hours. Apparently each ester groupundergoes hydrazinolysis to form the hydrazide releasing the alcoholwhich then esterifies another acetic acid group, which goes over to thehydrazide etc., until all the acetic acid groups have been converted.

At the end of the reaction the reaction mass comprises an aqueoussolution of the hydrazide containing free hydrazine and alcohol. It canbe used as such but it is desirably brought to approximate neutrality,e.g. a pH of about 5.5 to 9.5 and preferably about 8.5 by neutralizationwith an acid. Acetic acid is suitable but other acids are also useful,except that oxalic acid produces a crystalline precipitate. Citric acidis quite satisfactory.

In accordance with another aspect of the invention, to take fulladvantage of the excess hydrazine left at the end of reaction,additional amino-polyacetic acid can be added to react therewith,thereby increasing the sequestering capacity. This may itself serve asthe pH adjustment or such adjustment can now be effected.

In accordance with yet another aspect of the invention, the hydrazide tobe utilized is the carboxyhydrazide, i.e. a hydrogen of the terminal--NH₂ group of one or more hydrazide groups is replaced by --COOH. Suchproducts correspond to carbazic acids. Such conversion can be effectedby reacting the hydrazide with a carbonate, e.g. an alkali metalcarbonate such as potassium carbonate, and heating. Neutralization cannow be effected as indicated hereinabove.

The hydrazide solution can be employed directly or with dilution withoutseparation of by-products. The solution finds use where theamino-polyacetic acids themselves were theretofore employed, e.g.reverse osmosis modules and systems, flash and vapor compressionevaporators, heating and cooling systems, sea water feed heaters,cooling towers, ultrafiltration systems, heat exchangers, liquorevaporators, and the like, i.e. virtually all systems where scaledeposits and/or polyvalent heavy metal deposition might pose a problem.

The present invention also concerns a process for selectivelysequestering nickel from a mixture with iron, which process comprisescontacting such mixture with a composition comprising water and ahydrazide of an aminopolyacetic acid.

The invention will be further described in the following illustrativeexample wherein all parts are by weight unless otherwise expressed.

EXAMPLE 1

3.0 Liters of water and 0.25 liter of anhydrous methanol were added to areaction vessel and heated until the temperature reached 95° F. 6.67pounds of ethylenediaminetetraacetic acid were then added along with 3.7liters of 55% solution of hydrazine hydrate. The temperature rose to120° F. and was brought to 195° F. over 5.5 hours. After 13.5 hours at195° F. 3.38 pounds of nitrilotriacetic acid were added and, after a dayat 195°-200° F. 19.96 pounds of potassium carbonate were added. Thevessel was cooled to room temperature and its contents were 3.5 gallonscontaining 1.4 moles of chelant per liter. Citric acid was added tobring the pH to 8.5.

The chemical reactions involved in the foregoing example can besummarized as follows: ##STR1## which, upon reaction with potassiumcarbonate, gives the carbazic acid ##STR2##

The solution can be used per se or in diluted from. At chelantconcentration of about 4×10⁻³ or lower, per mole of chelant it willremove iron from scale and hold it in solution to the extent of 5 to 10moles of iron or more than 20 moles of calcium from a calcium sulfatescale.

The de-scaling activity can be seen in the following examples:

EXAMPLE 2

10 ml of the solution produced in Example 1 and diluted to contain perliter 0.2 mole of chelant and 0.3 mole of citric acid, pH 8.5, weremixed with 90 ml of water from an evaporator containing 36.8915 grams ofcalcium sulfate scale. The mass was held at 130° F. and the solids wereweighed periodically to ascertain any changes. The results obtained wereas follows:

    ______________________________________                                        Time in sol'n.                                                                             Wght of sample, g                                                                          Wght. loss, g                                       ______________________________________                                        Start        36.8915      --                                                  1 hour       35.9191      0.9723                                              2 hours      34.4425      2.3390                                              3 hours      32.8771      4.0144                                              18 hours     30.1140      6.7775                                              ______________________________________                                    

EXAMPLE 3

To a 100 ml solution which consisted of 3.9×10⁻⁵ moles of chelant asproduced in example 1 and 4.4×10⁻⁵ moles of citric acid for a final pHof 8.5, 0.0562 g of Fe₃ O4 was added.

The solution was heated to and maintained at a temperature of 130° F.for 16 hours at which time the solution was filtered and the ironcontent determined.

A spectrophotometric titration at 510 nm with 1,10 phenanthrolinerevealed that 2.31×10⁻⁴ moles of iron were dissolved in solution.

EXAMPLE 4

A 100 ml cleaning solution consisting of 7.8×10⁻⁴ moles of chelant asproduced in Example 1 and 8.6×10⁻⁴ moles of citric acid for a final pHof 8.5 was saturated with Fe₂ O₃, FeCr₂ O₄ 2H₂ O and Cr₂ O₃.

The solution was heated to and maintained at a temperature of 165° F.for 16 hours, after which iron and chromium content was determined.

The metal concentrations were determined via atomic absorptionspectrophotometry and found to be:

Iron: 4.66×1-⁻² Molar

Chromium: 3.33×10⁻³ Molar.

What is claimed is:
 1. A process for dissolving calcium sulfate scalefrom an article on which it is deposited which comprises contacting saidarticle with a composition comprising water and a hydrazide of anaminopolyacetic acid in an amount and for a time sufficient to dissolvethe calcium sulfate scale.
 2. A process for selectively sequesteringnickel from a solution or scale containing a mixture of nickel and ironwhich comprises contacting said solution or scale with a compositioncomprising water and a hydrazide of an aminopolyacetic acid in an amountand for a time sufficient selectively to sequester or dissolve thenickel.